Mourners in Newtown, Connecticut, hold signs during a solidarity vigil in memory of victims of the Las Vegas shooting.
Photograph: Michelle Mcloughlin/Reuters

The second amendment has become a badge and bumper sticker, a shield for gun activists and scripture for much of the American right. But like other cherished texts, it is not as clear as many make it out to be.

The amendment reads: “A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed.”

For most of the republic’s lifespan, from 1791 to 2008, those commas and clauses were debated by attorneys and senators, slave owners and freedmen, judges, Black Panthers, governors and lobbyists. For some, the militia was key; for others the right that shall not be infringed; for yet others, the question of states versus the federal government. For the most part, the supreme court stayed out it.

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“Americans have been thinking about the second amendment as an individual right for generations,” said Adam Winkler, a law professor at UCLA and author of Gunfight: The Battle over the Right to Bear Arms in America. “You can find state supreme courts in the mid-1800s where judges say the second amendment protects an individual right.”

But for the 70 years or so before a supreme court decision in 2008, he said, “the supreme court and federal courts held that it only applied in the context of militias, the right of states to protect themselves from federal interference”.

In 2008, the supreme court decided the District of Columbia v Heller, 5-4 , overturning a handgun ban in the city. The conservative justice Antonin Scalia wrote the opinion in narrow but unprecedented terms: for the first time in the country’s history, the supreme court explicitly affirmed an individual’s right to keep a weapon at home for self-defense.

Justice John Paul Stevens dissented, saying the decision showed disrespect “for the well-settled views of all of our predecessors on the court, and for the rule of law itself”. Two years later, he dissented from another decision favoring gun rights, writing:

The reasons that motivated the framers to protect the ability of militiamen to keep muskets, or that motivated the Reconstruction Congress to extend full citizenship to freedmen in the wake of the Civil War, have only a limited bearing on the question that confronts the homeowner in a crime-infested metropolis today.

This fight over history, waged by supreme court justices and unlikely allies and foes, goes all the way back.

“People look at the same record and come to wildly different conclusions about what the view was in the 18th century, in the 19th century,” said Nicholas Johnson, a Fordham University law professor who argues against Winkler’s view of 20th-century case law.

Attempts to parse “original” intent go all the way back to the revolution and its aftermath, when the country’s founders bickered about what exactly they were talking about. Carl Bogus, a law professor at Roger Williams University, has argued that James Madison wrote the second amendment in part to reassure his home state of Virginia, where slave owners were terrified of revolts and wary of northerners who would undermine the system.

“The militia were at that stage almost exclusively a slave-control tool in the south,” he said. “You gave Congress the power to arm the militia – if Congress chooses not to arm our militia, well, we all know what happens.”

The federalist Madison’s compromise, according to Bogus, was to promise a bill of rights. After weeks of tense debate, his federalists narrowly won the vote to ratify the constitution. “He writes an amendment that gives the states the right to have an armed militia, by the people arming themselves.”

A year later, the federal government passed a law requiring every man eligible for his local militia to acquire a gun and register with authorities. (The law was only changed in 1903.)

After the civil war, second amendment rights were again debated by Congress, which abolished militias in the former Confederate states and passed the 1866 Civil Rights Act, explicitly protecting freed slaves’ right to bear arms. A century later, the founders of the Black Panthers took up guns, symbolically and literally, to press for equal civil rights in California.

The state’s conservative lawmakers promptly took up the cause of gun control. In 1967, Governor Ronald Reagan signed the Mulford Act, banning the public carry of loaded guns in cities. The governor said he saw “no reason why on the street today a citizen should be carrying loaded weapons”.

Reagan later supported the Brady Act, a gun control law named after his aide, who was shot during an assassination attempt on Reagan in Washington DC. The National Rifle Association supported the Mulford Act but opposed the Brady Act, signed into law 26 years later.

Winkler, the UCLA professor, said that during the 1970s, a “revolt among the membership profoundly altered the NRA overnight. Since the 1930s, the group had supported restrictions on machine guns and public carry, but angry hardliners took control over the organization in 1977, when moderates wanted to retreat from lobbying work. The group then began a decades-long campaign to popularize its uncompromising positions.

“The NRA goes far beyond what the second amendment requires – people walking around with permits, on college campuses,” Winkler said. “Their argument is it’s a fundamental right and freedom. People care more about values than they care about policy.”

In the late 1990s, several prominent liberal attorneys, such as Laurence Tribe and Akhil Reed Amar, also argued for an individual right while advocating gun regulation. Gun control activists say they have not changed tack since the supreme court’s 2008 decision. Scalia wrote a narrow opinion and listed several exceptions, such as bans on “unusual and dangerous weapons” and sales to domestic abusers and people with mental illness. He also wrote that states and cities could ban firearms from places like government buildings.

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Lower courts have upheld many gun laws around the country since 2008, and the supreme court has declined to hear any second amendment cases since 2010. Attorneys and activists on both sides expect a looming fight over the right to carry guns in public, which the Heller decision does not address.

“The courts generally strike a balance between the need for lawmakers to protect public safety and this notion of second amendment rights,” said Avery Gardiner, co-president of the Brady Campaign to Prevent Gun Violence. The Heller decision, she said, was “entirely consistent” with gun laws like background checks.

“There’s a mythology here that the supreme court has said something about the second amendment that it hasn’t,” she said. “I think most Americans don’t like reading the footnotes.”